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United States Patent |
5,095,859
|
Iwata
,   et al.
|
March 17, 1992
|
SOHC type internal combustion engine
Abstract
A SOHC type internal combustion engine includes a pair of intake valves and
a pair of exhaust valves. The intake valve driving means comprises a
plurality of rocker arms disposed adjacent one another, including a pair
of driving rocker arms operatively connected separately to the intake
valves and a connection switchover mechanism capable of switching-over the
connection and disconnection of the adjacent rocker arms in accordance
with the operational condition of the engine. The exhaust valve driving
means comprises a pair of exhaust valve-side rocker arms operatively
connected separately to the exhaust valves and disposed on opposite sides
of the intake valve driving means in positions opposed to said cam shaft,
respectively. In the intake valve driving means, the opening and closing
mode of the intake valves can be changed in accordance with the
operational condition of the engine by operation of the connection
switchover mechanism, thereby providing an improvement in output from the
engine. The intake valve driving means is constructed compactly by
disposition of the plurality of rocker arms constituting the intake valve
driving means adjacent one another in the positions opposed to the cam
shaft, thereby enabling an effective and compact construction of the
connection switchover mechanism provided in the intake valve driving
means.
Inventors:
|
Iwata; Takeshi (Saitama, JP);
Aoki; Takatoshi (Saitama, JP);
Sugimoto; Chihaya (Saitama, JP)
|
Assignee:
|
Honda Giken Kogyo Kabushiki Kaisha (Tokyo, JP)
|
Appl. No.:
|
684657 |
Filed:
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April 12, 1991 |
Foreign Application Priority Data
Current U.S. Class: |
123/90.27; 123/90.16; 123/308 |
Intern'l Class: |
F01L 001/04; F01L 001/34 |
Field of Search: |
123/90.16,90.27,308
|
References Cited
U.S. Patent Documents
4553515 | Nov., 1985 | King et al. | 123/308.
|
4556025 | Dec., 1985 | Morita | 123/90.
|
4561391 | Dec., 1985 | Simko | 123/90.
|
4662323 | May., 1987 | Moriya | 123/90.
|
4671222 | Jun., 1987 | Gallot et al. | 123/90.
|
4741302 | May., 1988 | Oda et al. | 123/90.
|
4844022 | Jul., 1989 | Konno | 123/90.
|
4883027 | Nov., 1989 | Oikawa et al. | 123/90.
|
4979474 | Dec., 1990 | Morishita | 123/90.
|
4995352 | Feb., 1991 | Machino | 123/90.
|
Foreign Patent Documents |
0258061 | Mar., 1988 | EP.
| |
227911 | Sep., 1988 | JP | 123/90.
|
235645 | Sep., 1988 | JP | 123/90.
|
77738 | Mar., 1989 | JP | 123/90.
|
Primary Examiner: Gross; E. Rollins
Assistant Examiner: Lo; Weilun
Attorney, Agent or Firm: Lyon & Lyon
Claims
What is claimed is:
1. An SOHC type internal combustion engine comprising:
an intake valve driving means interposed between a single cam shaft
rotatably disposed above a combustion chamber and a pair of intake valves
for converting the rotational motion of the cam shaft into the opening and
closing motions of the intake valves;
an exhaust valve driving means interposed between the cam shaft and a pair
of exhaust valves for converting the rotational motion of the cam shaft
into the opening and closing motions of the exhaust valves; and
a plug-insertion cylindrical portion disposed in a cylinder head for
insertion of a spark plug at a central portion of a ceiling surface of
said combustion chamber, wherein
said intake valve driving means comprises a plurality of rocker arms
disposed adjacent one another and including a pair of driving rocker arms
operatively connected separately to the intake valves, and a connection
switchover mechanism capable of switching-over the connection and
disconnection of the adjacent rocker arms in accordance with the
operational condition of the engine, and
said exhaust valve driving means comprises a pair of exhaust valve-side
rocker arms operatively connected separately to the exhaust valves and
disposed on opposite sides of the intake valve driving means with respect
to said cam shaft.
2. An SOHC type internal combustion engine according to claim 1, wherein
said plug-insertion cylindrical portion is disposed in the cylinder head
to have an axis inclined so that an upper portion thereof is spaced from
the cam shaft between axes of the exhaust valves.
3. An SOHC type internal combustion, engine according to claim 1, wherein
said intake valve driving means comprises a first and a second driving
rocker arm which are operatively connected separately to the intake valves
and disposed adjacent each other, said first driving rocker arm including
a roller pinned thereon for rolling contact with a cam provided on the cam
shaft, said second driving rocker arm including a slipper provided thereon
for sliding contact with a raised portion provided on the cam shaft
adjacent said cam, said raised portion being formed to substantially
discontinue the opening and closing operation of the intake valve
operatively connected to the second driving rocker arm, when the
connection of the second and first driving rocker arms is released.
4. An SOHC type internal combustion engine according to claim 1, wherein
said intake valve driving means comprises a first and a second driving
rocker arm which are operatively connected separately to the intake
valves, and a free rocker arm disposed between the driving rocker arms and
capable being free from the intake valves, and the cam shaft is provided
with a first cam operative primarily for a high speed operation of the
engine, and a second cam adjacent the first cam and operative primarily
for low speed operation of the engine, and a raised portion adjacent the
first cam on an opposite side from the second cam, said free rocker arm
including a cam slipper provided thereon for sliding contact with said
first cam, said first driving rocker arm having a roller pinned thereon
for rolling contact with said second cam, said second driving rocker arm
including a slipper provided thereon for sliding contact with said raised
portion, and said raised portion being formed to substantially discontinue
the opening and closing operation of the intake valve operatively
connected to said second driving rocker arm when the connection of the
second driving rocker arm with the free rocker arm is released.
5. In an SOHC type internal combustion engine having a single cam shaft
rotatably mounted in a cylinder head above a combustion chamber, a pair of
intake valves mounted in said cylinder head on one side of said cam shaft,
a first pair of driving rocker arms operatively connecting said cam shaft
to said pair of intake valves separately, a pair of exhaust valves mounted
on said cylinder head on the other side of said cam shaft, a second pair
of driving rocker arms operatively connecting said cam shaft to said pair
of exhaust valves separately, and a spark plug mounting hole in a central
portion of a ceiling of the combustion chamber, an improvement comprising;
the first pair of driving rocker arms positioned between the second pair of
driving rocker arms, and
means for selectively connecting and disconnecting said first pair of
driving arms.
6. The SOHC type internal combustion engine according to claim 5 wherein a
spark plug insertion pipe is provided between said second pair of driving
rocker arms and extends to the spark plug mounting hole.
7. The SOHC type internal combustion engine according to claim 5 wherein a
free rocker arm is provided between said first pair of rocker arms and
said means also selectively connects and disconnects said free rocker arm
to the first pair of driving rocker arms.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the present invention is an single overhead cam (SOHC) type
internal combustion engine comprising an intake valve driving means
interposed between a single cam shaft rotatably disposed above a
combustion chamber and a pair of intake valves for converting the
rotational motion of the cam shaft into the opening and closing motions of
the intake valves, an exhaust valve driving means interposed between the
cam shaft and a pair of exhaust valves for converting the rotational
motion of the cam shaft into the opening and closing motions of the
exhaust valves, and a plug-insertion cylindrical portion for insertion of
a spark plug which is to be disposed at a central portion of a ceiling
surface of the combustion chamber.
2. Description of the Prior Art
Such SOHC type internal combustion engine is conventionally known, for
example, from Japanese Patent Application Laid-open No. 57806/88 and the
like.
In the above prior art, a plurality of intake valve-side rocker arms are
interposed between a pair of intake valves and a cam shaft, and a pair of
exhaust valve-side rocker arms are interposed between a pair of exhaust
valves and the cam shaft, so that the pair of intake valves and the pair
of exhaust valves are opened and closed by swingably driving the
individual rocker arms by cams provided on the cam shaft. In addition, a
connection switchover mechanism is provided in the intake valve-side
rocker arms and capable of switching-over the connection and disconnection
of the rocker arms, in order to improve the output performance of the
engine by varying the opening and closing mode of the intake valves in
accordance with the operational condition of the engine.
However, the intake valve-side rocker arms are adjacent one another in a
location in which the connection switchover mechanism is provided, but the
cams for the intake valve-side rocker arms and the cams for the exhaust
valve-side rocker arms are provided alternately in an axial direction on
the cam shaft and hence, the intake valve-side rocker arms cannot be
arranged in a compact manner. This provides an increase in size of the
connection switchover mechanism, resulting in an increase in weight of the
intake valve-side rocker arm, in a difficulty of improving the dimensional
accuracy of the connection switchover mechanism, and in a difficulty of
disposing the slide contact portion of the intake valve-side rocker arm
with the cam and the operatively connected position of the intake
valve-side rocker arm to the intake valve together in a plane
perpendicular to the swinging axis of the intake valve-side rocker arm,
thereby causing an uneven or eccentric load to act on the intake
valve-side rocker arm.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an SOHC
type internal combustion engine including a pair of intake valves and a
pair of exhaust valves, wherein the intake valve driving means can be
constructed compactly, whereby the opening and closing mode of the intake
valves can be changed in accordance with the operational condition of the
engine.
To achieve the above object, according to the present invention, there is
provided an SOHC type internal combustion engine comprising an intake
valve driving means interposed between a single cam shaft rotatably
disposed above a combustion chamber and a pair of intake valves for
converting the rotational motion of the cam shaft into the opening and
closing motions of the intake valves, an exhaust valve driving means
interposed between the cam shaft and a pair of exhaust valves for
converting the rotational motion of the cam shaft into the opening and
closing motions of the exhaust valves, and a plug-insertion cylindrical
portion disposed in a cylinder head for insertion or a spark plug which is
to be disposed at a central portion of a ceiling surface of the combustion
chamber, wherein the intake valve driving means comprises a plurality of
rocker arms disposed adjacent one another and including a pair of driving
rocker arms operatively connected separately to the intake valves, and a
connection switchover mechanism capable of switching-over the connection
and disconnection of the adjacent rocker arms in accordance with the
operational condition of the engine, and the exhaust valve driving means
comprises a pair of exhaust valve-side rocker arms operatively connected
separately to the exhaust valves and disposed on opposite sides of the
intake valve driving means with respect to the cam shaft.
With such construction, in the intake valve driving means, the opening and
closing mode of the intake valves can be changed in accordance with the
operational condition of the engine by switchingover the connection and
disconnection of the plurality of rocker arms by operation of the
connection switchover mechanism in accordance with the operational
condition of the engine. This can contribute to an improvement in output
from the engine. Moreover, the intake valve driving means can be
constructed compactly by disposition of the plurality of rocker arms
constituting the intake valve driving means adjacent one another in
positions along and the cam shaft. As a result, the connection switchover
mechanism provided in the intake valve driving means can be also
constructed compactly.
It is another object of the present invention to insure a space for
disposition of the plug insertion cylindrical portion, while providing a
compact entire valve-operating system.
It is a further object of the present invention to provide a reduction in
friction loss in the lower speed region in which the component, in the
valve-operating system, of the friction loss in the entire engine
constitutes a larger proportion and thus a reduction in friction loss in
the entire engine, and to provide a compact construction of the intake
valve driving means.
The above and other objects, features and advantages of the invention will
become apparent from a reading of the following description of the
preferred embodiments, taken in conjunction with the accompanying drawings
.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 to 4 illustrate a first embodiment of the present invention,
wherein
FIG. 1 is a longitudinal sectional view of an essential portion, taken
along a line I--I in FIG. 2;
FIG. 2 is a sectional view taken along a line II--II in FIG. 1;
FIG. 3 is a sectional view taken along a line III--III in FIG. 1; and
FIG. 4 is an enlarged sectional view taken along a line IV--IV in FIG. 1;
FIGS. 5 and 6 illustrate a second embodiment of the present invention,
wherein
FIG. 5 is a longitudinal sectional view of an essential portion, similar to
FIG. 1; and
FIG. 6 is a sectional view taken along a line VI--VI in FIG. 5;
FIGS. 7 to 9 illustrate a third embodiment of the present invention,
wherein
FIG. 7 is a longitudinal sectional view of an essential portion, similar to
FIG. 1;
FIG. 8 is a sectional view taken along a line VIII--VIII in FIG. 7;
FIG. 9 is a bottom view of a cylinder head, taken along a line IX--IX in
FIG. 7; and
FIG. 9A is a diagram illustrating the shape of a squish area;
FIG. 10 is a bottom view of a cylinder head, similar to FIG. 9, but
illustrating a modification of an intake passage;
FIGS. 11 and 12 illustrate a fourth embodiment of the present invention,
wherein
FIG. 11 is a longitudinal sectional view of an essential portion, similar
to FIG. 1; and
FIG. 12 is a sectional view taken along a line XIl--XII in FIG. 10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described by way of embodiments in
connection with the accompanying drawings.
Referring first to FIG. 1 illustrating a first embodiment of the present
invention, the essential portion of an engine body in an SOHC type
multi-cylinder internal combustion engine is comprised of a cylinder block
1 and a cylinder head 2 coupled to an upper surface of the cylinder block
1. A piston 4 having a depression 4a on an upper surface thereof is
slidably received in a cylinder 3 provided in the cylinder block 1, and a
combustion chamber 5 is defined between the upper surface of the piston 4
and the cylinder head 2.
Referring also to FIG. 2, first and second intake valve opening 6.sub.1 and
6.sub.2 and first and second exhaust valve openings 7.sub.1 and 7.sub.2
are provided in the cylinder head 2 and opened into a ceiling surface of
the combustion chamber 5. The intake valve openings 6.sub.1 and 6.sub.2
are connected to a single intake port 8 opened in one side surface of the
cylinder head 2, and the exhaust valve openings 7.sub.1 and 7.sub.2 are
connected to a single exhaust port 9 opened in the other side surface of
the cylinder head 2. A first V.sub.I1 and a second intake valve V.sub.I2
are slidably received in a pair of cylindrical guides 10 disposed in the
cylinder head 2, respectively, and adapted to open and close the first and
second intake openings 6.sub.1 and 6.sub.2 independently. Coiled valve
springs 12, 12 surrounding the intake valves V.sub.I1 and V.sub.I2 are
provided between the cylinder head 2 and retainers 11, 11 fixed to upper
ends of the intake valves V.sub.I1 and V.sub.I2 projecting from the
corresponding cylindrical guides 10, respectively, so that the intake
valves 12, 12 are biased upwardly, i.e., in valve-closing direction by the
valve springs 12, 12. Exhaust valves V.sub.E1 and V.sub.E2 capable of
opening and closing the first and second exhaust valve openings 7.sub.1
and 7.sub.2 independently are slidably received in a pair of cylindrical
guides disposed in the cylinder head 2. Coiled valve spring 15, 15
surrounding the exhaust valves V.sub.E1 and V.sub.E2 are provided between
the cylinder head 2 and retainers 14, 14 fixed to upper ends of the
exhaust valves V.sub.E1 and V.sub.E2 projecting from the cylindrical
guides 13, respectively, so that the exhaust valves V.sub.E1 and V.sub.E2
are based upwardly, i.e., in valve-closing direction by the valve springs
15, 15.
An intake valve driving means 17.sub.1, is interposed between the intake
valves V.sub.I1 and V.sub.I2 and a single cam shaft 16 operatively
connected to a crankshaft (not shown) at a reducing ratio of 1/2 for
converting the rotational motion of the cam shaft 16 into the opening and
closing motions of the intake valves V.sub.I1, and V.sub.I2, and an
exhaust valve driving means 18.sub.1 is interposed between the exhaust
valves V.sub.E1 and V.sub.E2 and the cam shaft 16 for converting the
rotational motion of the cam shaft 16 into the opening and closing motions
of the intake valves V.sub.E1 and V.sub.E2.
Referring also to FIG. 2, the cam shaft 16 is rotatably carried by the
cylinder head 2 and a holder 20 coupled to the cylinder head 2 and has a
horizontal axis perpendicular to the axis of the cylinder 3. The cam shaft
16 is integrally provided with a higher speed cam 21 and lower speed cams
22, 22 adjacent to opposite sides of the higher speed cam 21 and further
is integrally provided with exhaust valve cams 23, 23 on opposite sides
the lower speed cams 22, 22. The higher speed cam 21 has a shape
permitting the intake valves V.sub.I1 and V.sub.I2 to be opened and closed
in a higher speed operational region of the engine and includes a base
circle portion 21a and a raised portion 21b projecting radially outwardly
from the base circle portion 21a. Each of the lower speed cams 22 has a
shape permitting the intake valves V.sub.I1 and V.sub.I2 to be opened and
closed in a lower speed operational region of the engine and includes a
base circle portion 22a and a raised portion 22b projecting radially
outwardly of the cam shaft 16 in a projecting amount smaller than that of
the raised portion 21b of the higher speed cam 21 and over a region of a
central angle smaller than that of the raised portion 21b. Further, the
exhaust valve cam 23 has a shape permitting the exhaust valves V.sub.E1
and V.sub.E2 to be opened and closed in all the operational conditions of
the engine.
The intake valve driving means 17.sub.1 comprises a first driving rocker
arm 24.sub.1, operatively connected to the first intake valve V.sub.I1, a
second rocker arm 25.sub.1 operatively connected to the second intake
valve V.sub.12, and a free rocker arm 26.sub.1, disposed between the
driving rocker arms 24.sub.1 and 25.sub.1. The rocker arms 24.sub.1,
25.sub.1 and 26.sub.1 are swingably carried by a rocker arm shaft 27 which
is fixedly supported on a holder 20 and has an axis parallel to the cam
shaft 16 above the cam shaft 16. The exhaust valve driving means 18.sub.1
comprises a pair of exhaust valve-side rocker arms 29.sub.1 and 30.sub.1
swingably carried on a rocker arm shaft 28 which is fixedly supported on
the holder 20 parallel to the rocker arm shaft 27 above the cam shaft 16.
In the intake valve driving means 17.sub.1, a cam slipper 31 is provided at
one end of the first driving rocker arm 24.sub.1 and adapted to come into
sliding contact with the lower speed cam 22 provided on the cam shaft 16,
and a cam slipper (not shown) is provided at one end of the second driving
rocker arm 25.sub.1 to come into sliding contact with the lower speed cam
22 provided on the cam shaft 16. A cam slipper (not shown) is provided on
the free rocker arm 26.sub.1 to come into sliding contact with the higher
speed cam 21 provided on the cam shaft 16. In addition, a cam slipper 34
is provided on one end of each of the exhaust valve-side rocker arms
29.sub.1 and 30.sub.1 to come into sliding contact with corresponding one
of the exhaust valve cams 23, 23 provided on the cam shaft 16.
A tappet screw 35 is threadedly engaged in the other end of each of the
first and second driving arms 24.sub.1 and 25.sub.1 of the intake valve
driving means 17.sub.1 for advancing and retreating movement to abut
against an upper end of each of the intake valves V.sub.I1 and V.sub.I2,
so that the intake valves V.sub.I1 and V.sub.I2 are opened and closed in
response to the swinging movement of the driving rocker arms 24.sub.1 and
25.sub.1. A tappet screw 36 is also threadedly engaged in the other end of
each of the rocker arms 29.sub.1 and 30.sub.1 in the exhaust valve driving
means 18.sub.1 to abut against an upper end of each of the exhaust valves
V.sub.E1 and V.sub.E2, so that the exhaust valves V.sub.E1 and V.sub.E2
are opened and closed in response to the swinging movement of the rocker
arms 29.sub.1 and 30.sub.1.
Referring again to FIG. 1, a support plate 37 is fixedly mounted on the
holder 20 above the cylinder head 2 in a position corresponding to between
adjacent cylinders 3 to cover the rocker arm shafts 27 and 28. The support
plate 37 is provided with a lost motion mechanism 38 for resiliently
biasing the free rocker arm 26.sub.1 toward the higher speed cam 21.
The lost motion mechanism 38 comprises a bottomed cylindrical guide member
39 fitted in the support plate 37, a piston 40 slidably received in the
guide member 39 and having an abutment portion shaped convergently at an
end closer to the free rocker arm 26.sub.1 for abutment against the free
rocker arm 26.sub.1, a stopper 41 detachably secured to an inner surface
of the guide member 39 closer to an opened end to engage the piston 40,
and a first spring 42 and a second spring 43 interposed between the piston
40 and the guide member 39 to resiliently bias the piston 40 in a
direction to abut against the free rocker arm 26.sub.1.
The support plate 37 is provided with a bottomed cylindrical portion 37a
opened downwardly in a location corresponding to the free rocker arm
26.sub.1, and the guide member 39 is fitted into the bottomed cylindrical
portion 37a with its opened end turned downwardly. A spring chamber 44 is
defined between the piston 40 and the guide member 39. The first spring 42
has a relatively small spring constant and is provided in a compressed
manner between a retainer 45 contained in the spring chamber 44 and the
piston 40, and the second spring 43 has a relatively large spring constant
and is provided in a compressed manner between the retainer 45 and a
closed end of the guide member 39.
The bottomed small hole 40b is made coaxially in an inner surface of a
closed end of the piston 40, and the first spring 42 having a relatively
small spring constant is contained in the small hole 40b, whereby falling
of the first spring is prevented. The abutment portion 40a of the piston
40 also has an air vent hole 46 made therein into a cross-shape opening in
an outer surface of the abutment portion 40a and communicating with the
outside of the spring chamber 44, in order to prevent the interior of the
spring chamber 44 from being pressurized and depressurized during sliding
movement of the piston 40.
Further, an oil groove 47 is provided on the support plate 37 to extend in
parallel to the cam shaft 16 adjacent a base end of the bottomed
cylindrical portion 37a, and an oil passage 48 is provided in the base end
of the bottomed cylindrical portion 37a and the guide member 39 for
conducting an oil flowing through the oil groove 47 into the spring
chamber 44. Thus, lubricating oil can be supplied between the piston 40
and the guide member 39 by flowing of the lubricating oil through the oil
groove 47.
Referring to FIG. 4, the intake valve driving means 17.sub.1 is provided
with a connection switchover mechanism 50 capable of switching-over the
connection and disconnection of the rocker arms 24.sub.1 to 26.sub.1 in
accordance with the operational condition of the engine.
The connection switchover mechanism 50 comprises a first connecting piston
51 capable of connecting the first driving rocker arm 24.sub.1 and the
free rocker arm 26.sub.1, a second connecting piston 51 capable of
connecting the free rocker arm 26.sub.1 and the second driving rocker arm
25.sub.1, a restricting member 53 for restricting the movement of the
first and second connecting pistons 51 and 52, and a return spring 54 for
biasing the pistons 51 and 52 and the restricting member 53 toward a
disconnection position.
A first bottomed guide hole 55 is provided in the first driving rocker arm
24.sub.1 in parallel to the rocker arm shaft 27 and opened toward the free
rocker arm 26.sub.1. The first connecting piston 51 is slidably received
in the first guide hole 55, and a hydraulic pressure chamber 56 is defined
between one end of the first connecting piston 51 and a closed end of the
first guide hole 55. A communication passage 57 is also provided in the
first driving rocker arm 24.sub.1 to communicate with the hydraulic
pressure chamber 56, and a hydraulic pressure supply passage 58 is
provided in the rocker shaft 27 and leads to a hydraulic pressure supply
source which is not shown. The hydraulic pressure supply passage 58
continually communicates with the communication passage 57 and the
hydraulic pressure chamber 56 despite the swinging condition of the first
driving rocker arm 24.sub.1 by means of an internal groove (not numbered)
in the first driving rocker arm 24.sub.1.
A guide hole 59 corresponding to the first guide hole 55 is provided in the
free rocker arm 26.sub.1 to extend between opposite side surfaces thereof
in parallel to the rocker arm shaft 27, and the second connecting piston
52 abutting at one end thereof against the other end of the first
connecting piston 51 is slidably received in the guide hole 59.
A second bottomed guide hole 60 corresponding to the guide hole 59 is
provided in the second driving rocker arm 25.sub.1 in parallel to the
rocker arm shaft 27 and is open toward the free rocker arm 26.sub.1. The
bottomed cylindrical restricting member 53 abuts against the other end of
the second connecting piston 52 and is slidably received in the second
guide hole 60. The restricting member 53 is disposed with its open end
turned to the closed end of the second guide hole 60, and a collar 53a
projecting radially outwardly is in sliding contact with an inner surface
of the second guide hole 60 at such open end. The return spring 54 is
mounted in a compressed manner between the closed end of the second guide
hole 60 and a closed end of the restricting member 53, so that the pistons
51 and 52 and the restricting member 53 abut against one another and are
biased toward the hydraulic pressure chamber 56 by the spring force of the
return spring 54. Moreover, a communication hole 61 for venting air and
oil is provided at the closed end of the second guide hole 60.
A retaining ring 62 is fitted on an inner surface of the second guide hole
60 and is capable of engaging the collar 53a of the restricting member 53,
so that the restricting member 53 is inhibited from slipping out of the
second guide hole 60 by the retaining ring 62. Moreover, the fitted
position of the retaining ring 62 is determined to inhibit the further
movement of the restricting member 53 toward the free rocker arm 26.sub.1
from a state in which it is in abutment against the free rocker arm
26.sub.1 in a location corresponding to a plane between the free rocker
arm 26, and the second driving rocker arm 25.sub.1.
In the connection switchover mechanism 50, a swing pin 63 is embedded in
the side surface of each of the first and second driving rocker arms
24.sub.1 and 25.sub.1 which is facing the free rocker arm 26.sub.1 to
engage the free rocker arm 26.sub.1 while permitting the relatively
swinging movement of the driving rocker arms 24.sub.1 and 25.sub.1 with
the free rocker arm 26.sub.1.
Referring again to FIGS. 1 and 2, a spark plug 64 is disposed at a central
portion of a ceiling surface of the combustion chamber 5. A plug pipe 65
is disposed in the cylinder head 2 and serves as a cylindrical
plug-insertion portion for insertion of the spark plug 64. The pair of
exhaust valve-side rocker arms 29.sub.1 and 30.sub.1 constituting the
exhaust valve driving means 18.sub.1 are disposed for sliding contact with
the exhaust valve cams 23, 23 of the cam shaft 16 on opposite sides of the
intake rocker arms 24.sub.1, 25.sub.1 and 26.sub.1 which are disposed
adjacent one another to constitute the intake valve driving means
17.sub.1. This ensures that a relatively wide space is provided between
the exhaust valve rocker arms 29.sub.1 and 30.sub.1 and the exhaust valves
V.sub.E1 and V.sub.E2 can be disposed at a relatively wide distance apart
from each other. Therefore, the plug pipe 65 is positioned in the cylinder
head 2 in such a manner that the axis thereof is disposed between the
exhaust valves V.sub.E1 and V.sub.E2, i.e., located between the exhaust
valves V.sub.E1 and V.sub.E2 as well as between the exhaust valve-side
rocker arms 29.sub.1 and 30.sub.1. The plug pipe 65 is inclined so that
the upper portion thereof is spaced from the cam shaft 16. The spark plug
64 inserted into the plug pipe 65 is threadedly mounted in the cylinder
head 2 at the central portion of the ceiling surface of the combustion
chamber 5.
The operation of the first embodiment will be described. When the engine is
in a lower speed operation, the hydraulic pressure in the hydraulic
pressure chamber 56 in the connection switchover mechanism 50 is released,
and the pistons 51 and 52 and the restricting member 53 are in their
disconnected states in which they have been moved to the maximum extent
toward the hydraulic pressure chamber 56 by the spring force of the return
spring 54. In such condition, the abutment surfaces of the first and
second connecting pistons 51 and 52 are in positions between the first
driving rocker arm 24.sub.1 and the free rocker arm 26.sub.1, while the
abutment surfaces of the second connecting piston 52 and the restricting
member 53 are in positions between the free rocker arm 26.sub.1 and the
second driving rocker arm 25.sub.1. Therefore, the rocker arms 24.sub.1,
25.sub.1 and 26.sub.1 are in a disconnected state to allow relative
angular displacement.
In such disconnected condition, the rotation of the cam shaft 16 causes the
first and second driving rocker arms 24.sub.1 and 25.sub.1 to be swung in
response to the sliding contact with the lower speed cams 22, 22, so that
the intake valves V.sub.I1 and V.sub.I2 are opened and closed at a timing
and a lift amount corresponding to the shape of the lower speed cams 22,
22. During this time, the free rocker arm 26.sub.1 is swung in response to
the sliding contact with the higher speed cam 21, but the swinging
movement thereof exerts no influence on the first and second driving
rocker arms 24.sub.1 and 25.sub.1. In addition, the exhaust valves
V.sub.E1 and V.sub.E2 are opened and closed at a timing and a lift amount
corresponding to the shape of the exhaust valve cams 23, 23.
During a higher speed operation of the engine, a higher hydraulic pressure
is supplied to the hydraulic pressure chamber 56. This causes the first
and second connecting pistons 51 and 52 as well as the restricting member
53 in the connection switchover mechanism 50 of the intake valve driving
means 17.sub.1 to be moved toward the connecting positions against the
spring force of the return spring 54, so that the first connecting piston
51 is fitted into the guide hole 59, while at the same time, the second
connecting piston 52 is fitted into the second guide hole 60, thereby
connecting the rocker arms 24.sub.1, 25.sub.1 and 26.sub.1. At this time,
the amount of swinging movement of the free rocker arm 26.sub.1 in sliding
contact with the higher speed cam 21 is largest and therefore, the first
and second driving rocker arms 24.sub.1 and 25.sub.1 are swung with the
free rocker arm 26.sub.1, and the intake valves V.sub.I1 and V.sub.I2 are
opened and closed at a timing and a lift amount corresponding to the shape
of the higher speed cam 21.
During this higher speed operation, the exhaust valveside rocker arms
29.sub.1 and 30.sub.1 still open and close the exhaust valves V.sub.E1 and
V.sub.E2 at a timing and a lift amount corresponding to the shape of the
exhaust valve cams 23, 23, as during the lower speed operation.
It is possible to provide an improvement in output from the engine with a
valve operating characteristic adapted for the operational condition of
the engine by changing the opening and closing mode of the intake valves
V.sub.I1 and V.sub.I2 between the higher and lower speed operations in
this manner.
In such an internal combustion engine, in the position corresponding to the
cam shaft 16, the rocker arms 24.sub.1, 25.sub.1 and 26.sub.1 constituting
the intake valve driving means 17.sub.1 are disposed adjacent one another
and can be arranged together in a compact manner. It follows that the
connection switchover mechanism 50 is also arranged in a compact manner.
This enables not only an easy improvement in dimensional accuracy of the
components of the connection switchover mechanism 50 in order to provide a
smooth operation of the connection switchover mechanism 50, but also
contributes to a reduction in the weight of the rocker arms 24.sub.1,
25.sub.1 and 26.sub.1. Moreover, the sliding contact positions of the
first and second driving rocker arms 24.sub.1 and 25.sub.1 with the lower
speed cams 22, 22 and the operatively connected positions of these rocker
arms to the intake valves V.sub.I1 and V.sub.I2 can be established within
a plane substantially perpendicular to the axis of the rocker arm shaft
27, thereby avoiding the action of an uneven or eccentric load on the
first and second rocker arms 24.sub.1 and 25.sub.1.
The plug pipe 65 is disposed in the cylinder head 2 with its axis located
between the exhaust valves V.sub.E1 and V.sub.E2 thereby effectively
utilizing the space produced by positioning the exhaust valve-side rocker
arms 29.sub.1 and 30.sub.1 on opposite sides of the intake valve driving
means 17.sub.1. Therefore, it is possible to make the entire arrangement
more compact.
FIGS. 5 and 6 illustrate a second embodiment of the present invention,
wherein parts that are similar or identical to those in the previously
described first embodiment are identified by the same reference
characters.
A cam shaft 16 is rotatably carried by the cylinder head 2 and a cam holder
71 coupled to the cylinder head 2. Integrally provided on the cam shaft 16
in an arrangement similar to that shown in FIG. 3 illustrating the first
embodiment are a higher speed cam 21, lower speed cams 22, 22 on opposite
sides of the higher speed cam 21, and exhaust valve-side cams 23, 23 on
opposite sides of the lower speed cams 22, 22. A rocker arm shaft 70
parallel to the cam shaft 16 is fixedly supported in the cylinder head 2
below the cam shaft 16. An intake valve driving means 17.sub.2 is provided
between the intake valves V.sub.I1 and V.sub.I2 and the cam shaft 16 for
converting the rotational motion of the cam shaft 16 to the opening and
closing motions of the intake valves V.sub.I1 and V.sub.I2, and an exhaust
valve driving means 18.sub.2 is provided between the exhaust valves
V.sub.E1 and V.sub.E2 and the cam shaft 16 for converting the rotational
motion of the cam shaft 16 to the opening and closing motions of the
exhaust valves V.sub.E1 and V.sub.E2.
The intake valve driving means 17.sub.2 comprises a first driving rocker
arm 24.sub.2 operatively connected to the first intake valve V.sub.I1, a
second driving rocker arm 25.sub.2 operatively connected to the second
intake valve V.sub.I2, and a free rocker arm 26.sub.2 disposed between the
driving rocker arms 24.sub.2 and 25.sub.2. The rocker arms 24.sub.2,
25.sub.2 and 26.sub.2 are swingably carried at their base ends on the
rocker arm shaft 70. The exhaust valve driving means 18.sub.2 comprises
exhaust valve-side rocker arms 29.sub.2 and 30.sub.2 swingably carried at
their base ends on the rocker arm shaft 70 and operatively connected
separately to the exhaust valves V.sub.E1 and V.sub.E2.
In the intake valve driving means 17.sub.2, a cam slipper 72 is provided at
an intermediate and upper portion of the first driving rocker arm 24.sub.2
to come into sliding contact with the lower speed cam 22 (see FIG. 3); a
cam slipper 73 is provided at an intermediate and upper portion of the
second driving rocker arm 25.sub.2 to come into sliding contact with the
lower speed cam 22 (see FIG. 3), and a cam slipper 74 is provided on the
free rocker arm 26.sub.2 to come into sliding contact with the higher
speed cam 21 (see FIG. 3). In addition, cam slippers 75 and 76 are
provided on intermediate and upper portions of the exhaust valve-side
rocker arms 29.sub.2 and 30.sub.2 to come into sliding contact with the
exhaust valve cams 23, 23 (see FIG. 3).
A lost motion mechanism 38' having the basically same construction as the
lost motion mechanism 38 in the first embodiment is provided in the
cylinder head 2 to resiliently bias the free rocker arm 26.sub.2 in the
intake valve driving means 17.sub.2 toward the cam shaft 16.
Further, a connection switchover mechanism (not shown) having the basically
same construction as the connection switchover mechanism 50 in the first
embodiment is provided in the intake valve driving mechanism 17.sub.2 to
switchover the connection and disconnection of the rocker arms 24.sub.2,
25.sub.2 and 26.sub.2 in accordance With the operational condition of the
engine.
A lubricating oil supply passage 77 is provided in the rocker arm shaft 70
parallel to the hydraulic pressure supply passage 58, and injecting
nozzles 78 are provided at base portions of the rocker arms 24.sub.2,
25.sub.2, 26.sub.2, 29.sub.2 and 30.sub.2 respectively to communicate with
the lubricating oil supply passage 77 in accordance with the swing
positions of the rocker arms 24.sub.2, 25.sub.2, 26.sub.2, 29.sub.2 and
30.sub.2 in order to eject a lubricating oil from the lubricating oil
supply passage 77 toward their sliding contact portions with the cam shaft
16.
It should be noted that the pair of rocker arms 29.sub.2 and 30.sub.2
constituting the exhaust valve driving means 18.sub.2 are disposed on
opposite sides of the intake valve driving means 17.sub.2 in their
positions opposed to the cam shaft 16. Therefore, it is possible to insure
a relatively wide space between the exhaust valve-side rocker arms
29.sub.2 and 30.sub.2 as in the previous first embodiment and it is also
possible to dispose the exhaust valves V.sub.E1 and V.sub.E2 at a
relatively wide distance spaced from each other, so that the plug pipe 65
may be disposed in the cylinder head 2 between the exhaust valves V.sub.E1
and V.sub.E2 as well as between the exhaust valve-side rocker arms
29.sub.2 and 30.sub.2.
Thus, with such second embodiment, it is possible to insure a space for the
plug pipe 65 with a compact entire arrangement, notwithstanding the
provision of the connection switchover mechanism in the intake valve
driving means 17.sub.2.
FIGS. 7 to 9A illustrate a third embodiment of the present invention,
wherein parts similar or identical to those in the previous embodiments
are identified by the same reference characters.
Referring first to FIGS. 7 and 8, a cam shaft 16 is rotatably carried by a
cylinder head 2 and a holder 20 coupled to the cylinder head 2. An intake
valve driving means 17.sub.3 is provided between the cam shaft 16 and the
intake valves V.sub.I1 and V.sub.I2 for converting the rotational motion
of the cam shaft 16 into the opening and closing motions of the intake
valves V.sub.I1 and V.sub.I2, and an exhaust valve driving means 18.sub.3
is provided between the exhaust valves V.sub.E1 and V.sub.E2 and the cam
shaft 16 for converting the rotational motion of the cam shaft 16 into the
opening and closing motions of the exhaust valves V.sub.E1 and V.sub.E2.
The intake valve driving means 17.sub.3 comprises a first driving rocker
arm 24.sub.3 operatively connected to the first intake valve V.sub.I1, and
a second driving rocker arm 25.sub.3 operatively connected to the second
intake valve V.sub.I2 and disposed adjacent the first driving rocker arm
24.sub.3. The rocker arms 24.sub.3 and 25.sub.3 are swingably carried at
their intermediate portions by the rocker shaft 27. The exhaust valve
driving means 18.sub.3 comprises exhaust valve rocker arms 29.sub.3 and
30.sub.3 which are operatively connected separately to the exhaust valves
V.sub.E1 and V.sub.E2 and swingably carried at their intermediate portions
by the rooker arm shatt 28.
A connection switchover mechanism 50' is provided in the intake valve
driving means 17.sub.3 for switching-over the connection and disconnection
of the rocker arms 24.sub.3 and 25.sub.3 and comprises a connection piston
83 movable in responsive to a hydraulic pressure from the hydraulic
pressure supply passage 58 provided in the rocker arm shaft 27 between a
position in which the first and second driving rocker arms 24.sub.3 and
25.sub.3 are connected and a position in which such connection is
released, a restricting member 84 slidably received in the second driving
rocker arm 25.sub.3 and abutting against the connecting piston 83, and a
return spring 85 interposed between the restricting member 84 and the
second driving rocker arm 25.sub.3 to bias the connecting piston 83 and
the restricting member 84 toward a disconnecting side.
In the intake valve driving means 17.sub.3, a roller 81 is pinned at one
end of the first driving rocker arm 24.sub.3 to come into rolling contact
with the cam 79 integrally provided on the cam shaft 16, and a slipper 82
is provided at one end of the second driving rocker arm 25.sub.3 to come
into sliding contact with a raised portion 80 integrally provided on the
cam shaft 16 adjacent the cam 79. The raised portion 80 is basically
formed to have an outer surface that is circular about the axis of the cam
shaft 16, but also to have a shape such that the second intake valve
V.sub.I2 is slightly operated in an opening direction while being in a
substantially closed state, when the first intake valve V.sub.I1 is opened
by the first driving rocker arm 24.sub.3 in a condition in which the
second driving rocker arm 25.sub.3 is not connected with the first driving
rocker arm 24.sub.3. Moreover, the width of the raised portion 80 in a
direction along the axis of the cam shaft 16 is relatively small, and the
width of the slipper 82 provided on the second driving rocker arm 25.sub.3
is also small in correspondence to the raised portion 80 because very
little force is transmitted therebetween.
Rollers 86 and 87 are pinned at one end of each of the exhaust valve-side
rocker arms 29.sub.3 and 30.sub.3 in the exhaust valve driving means
18.sub.3 to come into rolling contact with the exhaust valve-side cams 23,
23 provided on the cam shaft 16 on opposite sides of the cam 79 and the
raised portion 80 provided on the cam shaft 16 adjacent each other,
respectively.
Thus, the pair of the exhaust valve-side rocker arms 29.sub.3 and 30.sub.3
constituting the exhaust valve driving means 18.sub.3 are disposed on
opposite sides of the intake valve driving means 17.sub.3 in their
position opposed to the cam shaft 16, and therefore, it is possible to
insure a relatively wide space between the exhaust valve rocker arms
29.sub.3 and 30.sub.3. It is also possible to dispose the exhaust valves
V.sub.E1 and V.sub.E2 at a relatively wide distance spaced apart from each
other, so that the plug pipe 65 may be disposed in the cylinder head 2
between the exhaust valves V.sub.E1 and V.sub.E2 as well as between the
exhaust valve-side rocker arms 29.sub.3 and 30.sub.3.
Referring also to the FIG. 9, an intake passage 97.sub.1 provided in the
cylinder head 2 in communication with the first intake valve opening
6.sub.1 and an intake passage 97.sub.2 provided in the cylinder head 2 in
communication with the second intake valve opening 6.sub.2 are commonly
connected to an intake port 8 provided in one side surface of the cylinder
head 2 for each cylinder 3. One of the intake passages, such as passage
97.sub.1, is formed in an inwardly expanded and curved fashion to extend
along the inner surface of the combustion chamber 5 just in front of the
first intake valve opening 6.sub.1, in order to provide a swirl suction of
the gas from the first intake valve opening 6.sub.1 into the combustion
chamber 5, when the second intake valve V.sub.I2 has become substantially
inoperative.
A recess 2a is provided on a lower surface of the cylinder head 2 to form a
ceiling surface of the combustion chamber 5, and a squish area 98 is
provided between an opened edge of the recess 2a and a top surface of the
piston 4 at the top dead center point. The opened edge of the recess 2a is
shaped such that the following edge portions are connected together: a
first peripheral edge 2a.sub.1 corresponding to an inner periphery of the
cylinder extending from the first intake valve opening 6.sub.1 to the
first exhaust valve opening 7.sub.1 in a direction 99 of swirl suction
from the first intake valve opening 6.sub.1 into the combustion chamber 5;
a second peripheral edge portion 2a.sub.2 corresponding to a peripheral
edge of the circular depression 4a in the piston 4 between the first and
second exhaust valve openings 7.sub.1 and 7.sub.2 ; a third peripheral
edge portion 2a.sub.3 irregularly connected between an inner periphery of
the cylinder and the peripheral edge of the depression 4a between the
second exhaust valve opening 7.sub.2 and the second intake valve opening
6.sub.2 ; and a fourth peripheral edge portion 2a.sub.4 corresponding to
the peripheral edge of the depression 4a between the second and first
intake valve opening 6.sub.2 and 6.sub.1. Therefore, the squish area 98
has a shape as shown by the cross-hatched region in FIG. 9A and is not
formed in a section extending from the first intake valve opening 6.sub.1
to the first exhaust valve opening 7.sub.1 in the direction 99 of swirl
suction. In those portions of the squish area 98 which correspond to
between the intake valve openings 6.sub.1 and 6.sub.2 and between the
exhaust valve openings 7.sub.1 and 7.sub.2, the inner periphery of the
squish area 98 is opposed to the peripheral edge of the recess 4a at the
upper and central portion in the piston 4.
With such third embodiment, in a higher speed operation condition of the
engine, the first and second driving rocker arms 24.sub.3 and 25.sub.3 can
be interconnected, so that the intake valves V.sub.I1 and V.sub.I2 can be
opened and closed at a timing and a lift amount suitable for higher speed
operation by the shape of the cam 79. On the other hand, in a lower speed
operational condition of the engine, the connection of the first and
second driving rocker arms 24.sub.3 and 25.sub.3 can be released, so that
the first intake valve V.sub.I1 can be opened and closed at the timing and
lift amount corresponding to the shape of the cam 79 by the first driving
rocker arm 24.sub.3 in slide contact with the cam 79, while the second
driving rocker arm 25.sub.3 in slide contact with the raised portion 80
can be brought into a substantially inoperative state to put the second
intake valve V.sub.I2 substantially out of operation. However, the second
intake valve V.sub.I2 is not completely inoperative and can be slightly
operated in the opening direction when the first intake valve V.sub.I1 is
opened. This makes it possible to prevent sticking of the second intake
valve V.sub.I2 to the valve seat which may be otherwise produced when a
completely closed state is maintained.
In the lower speed operational condition of the engine in which the second
intake valve V.sub.I2 is substantially inoperative and only the first
intake valve V.sub.I1 is opened and closed, a fuel-air mixture from the
intake port 8 is supplied via the intake passage 97.sub.1 and the first
intake valve opening 6.sub.1 into the combustion chamber 5, so that a
swirl is produced in the combustion chamber 5. Moreover, the intake
passage 97.sub.1 is formed in a curved fashion to extend tangentially
along the inner surface of the combustion chamber 5 just in front of the
first intake valve opening 6.sub.11, so that the fuel-air mixture is drawn
into the combustion chamber 5 while being whirled, enabling a swirl to be
produced effectively.
The fuel-air mixture introduced into the combustion chamber 5 through the
first intake valve opening 6.sub.1 flows within the combustion chamber 5
in the direction of swirl suction, but because the squish area 98 is not
formed in the section from the first intake valve opening 6.sub.1 to the
first exhaust valve opening 7.sub.1 in the direction 99 of swirl suction,
a squish flow can be prevented from acting on the whirled flow just
introduced into the combustion chamber 5 through the first intake valve
opening 6.sub.1 in a direction that otherwise would disturb the whirling
of such flow, thereby effectively forming a swirl in the combustion
chamber 5.
Further, the inner periphery of the squish area 98 is formed in opposition
to the peripheral edge of the depression 4a at the central portion of the
upper surface of the piston 4 between the intake valve openings 6.sub.1
and 6.sub.2 as well as between the exhaust valve openings 7.sub.1 and
7.sub.2 and therefore, a whirled flow is easily produced along the inner
surface of the combustion chamber 5, which makes it possible to form a
more effective swirl within the combustion chamber 5.
It is possible to provide an improvement in burning property by forming a
powerful swirl within the combustion chamber 5 in this manner.
It should be noted that the first driving rocker arm 24.sub.3 which is in
operation in a lower speed region in which the component, in the valve
operating system, of the friction loss in the entire engine constitutes a
larger proportion is in rolling contact with the cam 79 through the roller
81, and this can contribute to a reduction in friction loss due to the
valve operating system in the lower speed region and thus a reduction in
friction loss in the entire engine. Moreover, because the exhaust
valve-side rocker arms 29.sub.3 and 30.sub.3 constituting the exhaust
valve driving means 18.sub.3 is also in rolling contact with the exhaust
valve cams 23, 23 through the rollers 86 and 87, it is possible to further
reduce the friction loss in the lower speed region.
Further, the second driving rocker arm 25.sub.3 is in slide contact with
the raised portion 80 through the slipper 83 and this ensures that the
width of the slipper 83 can be smaller than that of the roller 81.
Moreover, because the intake valve driving means 17.sub.3 is comprised of
the pair of driving rocker arms 24.sub.3 and 25.sub.3, such intake valve
driving means 17.sub.3 can be constructed more compactly along the axis of
the cam shaft 16, as compared with the intake valve driving means
constructed of three rocker arms as in the previously described first and
second embodiments.
Moreover, as in the previous embodiments, the entire construction can be
made compact, notwithstanding the provision of the connection switchover
mechanism 50' in the intake valve driving means 17.sub.3.
In the above third embodiment, the intake passage 97.sub.1 has been formed
in the curved fashion just in front of the first intake valve opening
6.sub.1, but it will be understood that the intake passage 97.sub.1 may be
disposed with the position of the intake port 8 being displaced toward the
second intake valve opening 6.sub.2, as compared with FIG. 9, so as to
extend substantially along the inner surface of the combustion chamber 5
over the entire length of the passage from the connection with the intake
port 8 to the first intake valve opening 6.sub.1.
FIG. 11 and 12 illustrate a fourth embodiment of the present invention,
wherein parts that are similar or identical to those in the previous
embodiments are identified by the same reference characters.
An intake valve driving means 17.sub.4 is provided between the cam shaft 16
and the intake valves V.sub.I1 and V.sub.I2 for converting the rotational
motion of the cam shaft 16 into the opening and closing motions of the
intake valves V.sub.I1 and V.sub.I2, and an exhaust valve driving means
18.sub.4 is provided between the exhaust valves V.sub.E1 and V.sub.E2 and
the cam shaft 16 for converting the rotational motion of the cam shaft 16
into the opening and closing motions of the exhaust valves V.sub.I1 and
V.sub.E2.
The intake valve driving means 17.sub.4 comprises a first driving rocker
arm 24.sub.4 operatively connected to the first intake valve V.sub.I1, a
second driving rocker arm 25.sub.4 operatively connected to the second
intake valve V.sub.I2, and a free rocker arm 26.sub.4 disposed between the
driving rocker arms 24.sub.4 and 25.sub.4 and capable of becoming free
from the intake valves V.sub.I1 and V.sub.I2. The rocker arms 24.sub.4,
25.sub.4 and 26.sub.4 are swingably carried at their intermediate portions
by the rocker arm shaft 27. The exhaust valve driving means 18.sub.4
comprises exhaust valve-side rocker arms 29.sub.4 and 30.sub.4 which are
operatively connected separately to the exhaust valves V.sub.E1 and
V.sub.E2 and swingably carried at their intermediate portions by the
rocker arm shaft 28.
A connection switchover mechanism 50 is provided in the intake valve
driving means 17.sub.4 and is capable of switching-over the connection and
disconnection of the rocker arms 24.sub.4, 25.sub.4 and 26.sub.4.
Integrally provided on the cam shaft 16 are a higher speed cam 21 formed
so that it is operative primarily during a higher speed operation of the
engine, a lower speed cam 22 as a second cam formed adjacent the higher
speed cam 21, so that it is operative primarily during a lower speed
operation of the engine, and a raised portion 80 adjacent the higher speed
cam 21 on the opposite side from the lower speed cam 22. Further, in the
intake valve driving means 17.sub.4, a roller 89 is pinned at one end of
the first driving rocker arm 24.sub.4 to come into rolling contact with
the lower speed cam 22; a slipper 90 is provided at one end of the free
rocker arm 26.sub.4 to come into sliding contact with the higher speed cam
21, and a slipper 91 is provided at one end of the second driving rocker
arm 25.sub.4 to come into sliding contact with the raised portion 80.
Moreover, the width of the raised portion 80 in a direction along the axis
of the cam shaft 16 is relatively small, and the width of the slipper 91
provided on the second rocker arm 25.sub.4 is also small in correspondence
to the raised portion 80.
Rollers 86 and 87 are pinned at one end of each of the exhaust valve-side
rocker arms 29.sub.4 and 30.sub.4 in the exhaust valve driving means
18.sub.4 to come into rolling contact with the exhaust valve cams 23, 23
provided on the cam shaft 16 on opposite sides of the lower speed cam 22
and the raised portion 80, respectively.
Thus, the pair of exhaust valve-side rocker arms 29.sub.4 and 30.sub.4
constituting the exhaust valve driving means 18.sub.4 are disposed on
opposite sides of the intake valve driving means 17.sub.4 in positions
opposed to the cam shaft 16 and therefore, it is possible to insure a
relatively wide space between the exhaust valve rocker arms 29.sub.4 and
30.sub.4. In addition, the exhaust valves V.sub.E1 and V.sub.EZ can be
disposed at a relatively large distance apart from each other, so that the
plug pipe 65 may be positioned in the cylinder head 2 between the exhaust
valves V.sub.E1 and V.sub.E2 as well as between the exhaust valve-side
rocker arms 29.sub.4 and 30.sub.4.
With such fourth embodiment, in a higher speed operational condition of the
engine, the first and second driving rocker arms 24.sub.4 and 25.sub.4 and
the free rocker arm 26.sub.4 are interconnected, so that the intake valves
V.sub.I1 and V.sub.I2 can be opened and closed at a timing and a lift
amount corresponding to the shape of the higher speed cam 21. In a lower
speed operational condition of the engine, the connection of the first
driving rocker arm 24.sub.4 and the free rocker arm 26.sub.4 as well as
the connection of the free rocker arm 26.sub.4 and the second driving
rocker arm 25.sub.4 can be released, so that the first intake valve
V.sub.I1 can be opened and closed at a timing and a lift amount
corresponding to the shape of the lower speed cam 22 by the first driving
rocker arm 24.sub.4 which is in rolling contact with the lower speed cam
22, while the second driving rocker arm 25.sub.4 in sliding contact with
the raised portion 80 can be brought into a substantially inoperative
state to put the second intake valve V.sub.I2 substantially out of
operation.
The first driving rocker arm 24.sub.4 operative in a lower speed region is
in rolling contact with the lower speed cam 22 through the roller 89,
which can contribute to a reduction in friction loss in the
valve-operating system in the lower speed region and thus a reduction in
friction loss in the entire engine. In addition, because the exhaust
valve-side rocker arms 29.sub.4 and 30.sub.4 are also in rolling contact
with the exhaust valve cam 23, 23 through the rollers 86 and 87, it is
possible to provide a further reduction in friction loss in the lower
speed region.
Further, the second driving rocker arm 25.sub.4 is in sliding contact with
the raised portion 80 through the slipper 91 and therefore, the width of
the slipper 91 can be smaller than that of the roller 89. This ensures
that the intake valve driving means 17.sub.4 can be constructed more
compactly along the axis of the cam shaft 16, as compared with those in
the previous first and second embodiments.
Moreover, the entire arrangement can be made compact as in the previous
embodiments, notwithstanding the provision of the connection switchover
mechanism 50 in the intake valve driving means 17.sub.4.
In the foregoing embodiments, the connection switchover mechanism has been
described as being provided in the rocker arms constituting the intake
valve driving means for switching-over the connection and disconnection of
all the rocker arms, but it will be understood that the connection
switchover mechanism may be constructed to switch-over the connection and
disconnection of only a pair of adjacent rocker arms.
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